1. Technical Field
The present invention relates to a novel structure and method for applying a lining material to reinforce pipelines such as a gas conduit, a city water pipe, a sewage pipe, pipelines for laying telecommunication cables or electric cables, and particularly, pipelines embedded in the ground. More particularly, the present invention relates to a technical means suitable for applying a lining material to a gas conduit or intermediate line with a working pressure of approximately 3 to 10 kg/cm.sup.2.
2. Background Art
A conventional method for applying a lining material to an underground pipeline comprises the steps of depositing a hermetic film on the outer surface of a tubular fiber reinforcement material composed of a tubular woven or unwoven fabric, or a combination of tubular woven and unwoven fabrics superimposed one over the other to provide a lining material, applying a thermosetting resin liquid to the inner surface of the lining material and impregnating the thermosetting resin liquid into the tubular fiber reinforcement material, inserting the lining material into the pipeline while the lining material is being reversed under a fluid pressure, pressing the lining material against the inner surface of the pipeline under the fluid pressure, curing the thermosetting resin liquid so as to adhesively attach the lining material to the inner surface of the pipeline, and causing the thermosetting resin liquid and the tubular fiber reinforcement material to cooperate together to provide a rigid FRP (FIBER-REINFORCED PLASTICS) tube within the pipeline.
This method attempts to reduce the adhesive force between the lining material and the inner surface of the pipeline so as to prevent the lining material from cracking as the pipeline is damaged, or the joints from detaching due to earthquake or the like. This method also utilizes high strength fiber such as a glass fiber or an aromatic polyamide fiber on the circumference of the lining material so as to withstand internal or external pressure and insure a fluid path if the lining material is exposed as a result of damage to the pipeline (see U.S. Pat. No. 5,164,237).
Such a lining method is effective in the case that the pipeline is composed of cast iron pipes or fume pipes, but is not sufficiently effective particularly when it is applied to a steel pipe such as a gas conduit with an intermediate working pressure of approximately 3 to 10 kg/cm.sup.2 (hereinafter, referred to as an "intermediate pressure A line").
The intermediate pressure A line uses carbon steel pipes which have a high strength and tenacity. These pipes are welded together to form a long pipeline system. Bent pipes are welded to bent portions of the pipeline to provide an integral pipeline system. With such a pipeline system, if the ground is liquified or subjected to contraction due to earthquake, the resulting stress tends to be concentrated on the bent portions.
FIG. 3 shows the manner in which the bent portion of the intermediate pressure A line fractures. FIG. 3(a) shows a bent portion 2 of a pipeline 1. When the ground contracts due to an earthquake or the like, the pipeline 1 is repeatedly extended and contracted in a longitudinal direction. This results in a change in the angle of the bent portion 2. This change causes the bent portion 2 to be significantly deformed in the direction in which it is bent and extended. If the bent angle .alpha. of the bent portion 2 increases, the bent portion 2 is urged into the pipe. If the bent angle a of the bent portion 2 decreases when the bent portion 2 is extended, a portion of the bent portion which has been urged into the pipe is subject to extension. When the bent portion 2 is locally deflected to a substantial extent, a large crack 3 occurs within the bent portion 2 due to fatigue, as shown in FIG. 3(b).
In the case that a lining material 4 is adhered to the inner surface of the pipeline 1, the edge of the crack 3 is bent inwardly to produce sharp burrs 5. These burrs 5 break the lining material 4 as shown in FIG. 3(c). Thus, damage to the pipeline 1 causes corresponding damage to the lining material 4.
A cast iron pipe has a low tenacity. Thus, if a cast iron pipe fractures, burrs 5 are rarely produced. Thus, a fluid path can be maintained since the lining material 4 is free from damage. On the other hand, a steel pipe has a high tenacity. Thus if a shock load is applied to a steel pipe, it will not fracture as opposed to the cast iron pipe. However, a crack 3 is likely to occur when local stress is concentrated on the bent portion 2. The resulting burrs 5 will cause damage to the lining material 4.
An adhesive or a seal is applied to the end of the lining material within the pipeline so as to prevent the entry of a fluid between the lining material and the pipeline. Normally, a metal ring is fit within the end of the lining material. The metal ring is extended to thereby press the end of the lining material against the inner surface of the pipeline (see JP, B, Sho. 60-41276).
With this treatment, however, the pipeline and the lining material is subjected to displacement if significant damage to the pipeline occurs. If the end of the lining material is displaced relative to the pipeline, the seal is damaged. A fluid then enters between the lining material and the pipeline and may flow out of a portion of the pipeline thus damaged.